1. Field of the Invention
The present invention generally relates to analog-to-digital and digital-to-analog converter circuits, and more particularly, to C-2C analog-to-digital and digital-to-analog converters wherein a capacitance ladder network is formed using monolithic, multilayer fabrication techniques and can be trimmed or adjusted electrically after manufacture to obtain desired tolerances.
2. Description of the Prior Art
The advantages of digital control, computation and communication are being applied to many diverse fields. These applications, however, often require analog-to-digital (A/D) and digital-to-analog (D/A) signal conversion. A/D and D/A converters using resistor ladder networks are well known and widely used. While these resistor ladder networks have been satisfactory for many applications, they have several disadvantages. Such networks must be made with many sections and, even then must be matched or trimmed to attain the desired accuracy. As a result, resistor ladder networks used in A/D and D/A converters are expensive to manufacture both in terms of parts and time of adjustment. In addition, resistor ladder networks are difficult to manufacture using integrated circuit techniques, and their maximum speed is limited by the time constant of the resistors and their associated distributed and parasitic capacitances.
More recently, capacitor ladder networks have been used in A/D and D/A converters. These networks offer the advantages of lower cost and higher speed of operation. An example of such a capacitor ladder network is disclosed in U.S. Pat. No. 3,665,458 to Mulkey et al. Mulkey et al. disclose a capacitor ladder switching network which may be fabricated using thin film techniques; but while a distinct improvement over prior art resistor ladder network, the Mulkey et al. capacitor ladder network is not compatible with integrated circuit fabrication techniques and has no provision for trimming or adjustment.